‘Volcanic Unrest’ at Alaska’s Mount Spurr Suggests 50-50 Chance an Eruption Could Be Coming

A volcano in southern Alaska is rumbling with seismic activity, which hints at the possibility that it might soon erupt.

Mount Spurr, an 11,070-foot-tall stratovolcano roughly 75 miles from Anchorage, has been experiencing earthquakes since last April—a phenomenon that researchers call “volcanic unrest.”

In recent months, these earthquakes have been occurring more frequently, rising from an average of roughly 30 per week to 125 per week. In total, researchers have recorded more than 2,700 earthquakes. The largest was a magnitude 2.9 quake on January 2.

“The duration (ten months) and nature of the unrest suggest that an eruption is possible,” according to a February 6 statement from the United States Geological Survey’s Alaska Volcano Observatory.

Volcanologists expect to see some warning signs that the volcano is about to erupt—more seismic activity, gas emissions, surface heating and changes to surface deformation, for example—if an eruption does occur. These indicators may offer “days to a few weeks” of advanced notice, they write, “but that is not certain.”

Scientists are also keeping an eye out for a tremor, or a period of sustained seismic activity in which the volcano “just begins to shake continuously,” says Matt Haney, the scientist-in-charge of the Alaska Volcano Observatory, to Melissa Frey of Alaska’s News Source.

“We expect … more indications in our data prior to an eruption that would give us more indication that the odds were increasing of an eruption,” Haney adds. “We haven’t seen those yet.”

If the snow- and ice-covered volcano does erupt, scientists expect the blast to occur at a site called Crater Peak. That’s because the summit hasn’t erupted for thousands of years, and the earthquakes have been moving away from the summit crater and down toward Crater Peak. Situated about two miles below Spurr summit, this vent erupted most recently in 1992 and 1953. During each of those incidents, the volcano spewed ash 65,000 feet into the air.

If Crater Peak erupts again, scientists expect it to release streams of hot gas, rock and ash traveling at speeds of more than 200 miles per hour. The super-heated materials would likely melt the snow and ice covering the volcano’s surface, resulting in mudflows known as “lahars.”

Fortunately, very few people live in the shadow of Mount Spurr, so it’s unlikely that the pyroclastic flows or lahars would harm any residents or structures. The biggest impact would likely be ash: When Crater Peak erupted in 1992, for example, it blanketed the city of Anchorage in a thin layer of ash that shut down the airport.

The 1992 eruption cost the city of Anchorage nearly $2 million in cleanup, office closures and damage, according to the National Oceanic and Atmospheric Administration’s National Centers for Environmental Information. No one died during the eruption itself, but one person did suffer a fatal heart attack while shoveling the ash.

“Today there are even more flights coming in and out of the Anchorage airport, so if something like that were to happen, that would be very disruptive,” Haney tells Live Science’s Stephanie Pappas.

Mt. Spurr, Alaska, eruption. August 18, 1992.

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It’s also possible that Mount Spurr will simply quiet down without erupting. That has happened in the past, including between 2004 and 2006, when the volcano experienced a lot of earthquakes but ultimately never erupted.

“Sometimes there can be a build-up of magma beneath the volcano, but it doesn’t have enough magma to ultimately proceed all the way and produce a volcanic eruption,” Haney tells Alaska’s News Source.

Right now, volcanologists say there’s a roughly 50-50 chance of an eruption at Crater Peak. In the meantime, they’re doing everything they can to monitor Mount Spurr, including analyzing seismic data from 11 stations. They’re also flying over the volcano to take gas measurements and removing snow from instruments.

“We’re watching it very closely,” Haney tells the Alaska Beacon. “We’re saying that there’s unrest above background [levels], but it’s uncertain if this is actually building to an eruption.”

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Sarah Kuta is a writer and editor based in Longmont, Colorado. She covers history, science, travel, food and beverage, sustainability, economics and other topics.